In a way, that’s accurate. PFF grades based on if they believe a player did his job on a play. If the playcall is bad (i.e, no one is open), then they’re not gonna ding the QB for throwing it away.
I’ve said before that PFF should never be viewed as gospel. There are too many variables they can’t possibly know. But at the very least, I think it’s decent evidence that there’s a lot more holding us back before you hit QB play on the list.